Because of advances in the state of the art of semiconductor technology in terms of size, cost, and power-consumption reduction, it is advantageous to incorporate digital processing and computational systems into electrical apparatus of all kinds. A problem associated with such systems is that when operating power is interrupted or turned off, data contained in system memories is lost. This problem was solved to some extent by providing back-up battery power to the memory devices to preserve the data stored therein. A further problem, however, is to ensure that the stored data is correct or valid upon re-application of operating power. It has been suggested to store a known data word and verify it as being valid before any data processing is recommenced. However, such a known data word may always be the same and may always be stored at the same memory location, and through some undetermined physical characteristic associated with the memory device, the storage location of the memory device may take a set of the known data word, analogous to a stored latent image on a display device. This leads to the danger of the known data word being produced by the memory for verification upon reapplication of operating power, even though the contents of the memory may have been destroyed during the loss of operating power.